In a standard shuttleless loom a weft yarn is pulled from a supply spool by a mechanical feeder and fed through a fixed-resistance mechanical brake to a nozzle that is directed crosswise through a shed formed between upper and lower groups of warp yarns. Inside the shed the yarn is guided along a passage formed by the teeth of a confining comb mounted on a support along with the beating comb. The yarn is moved the entire weftwise width of the fabric by relay nozzles spaced along the shed and pressurized sequentially. At the downstream edge of the goods the yarn is trapped by a weft-yarn aspirator and held thereby.
Occasionally the weft yarn, called the pick when inserted into the shed, breaks and this breakage is detected by a photocell arrangement. French patents 2,537,168 and 2,583,435 describe mechanical arrangements for extracting the pick, a job that is particularly difficult after it has been beaten into the warp by the comb. First the defective pick must be stripped off the preceding pick, typically by a system of needles, and then it must be pulled weftwise out of the fabric, for instance by a pincher-type gripper. Such arrangements do not allow a pick that has been broken into several pieces to be extracted fully, and are normally unable to actually unweave a portion of the fabric, that is strip out several successive bad picks.
In European patent application 100,939 (see U.S. Pat. No. 4,502,512) a combined pneumatic/mechanical system is employed to separate out a bad pick and pull it out of the goods. The mechanical elements can damage the goods and, like the preceding arrangements, the device has a problem when the actual location where the pick is beaten moves somewhat, as is common in weaving.